That's when hybrid drivers, who were previously allowed to enter central London's Congestion Charge zone without paying the stiff fees (now £11.50, or roughly $16.50) that are levied on conventional vehicles during weekday business hours, have to start paying up.

The old system of charges permitted vehicles with emissions rated at 75 to 100 grams of CO2 per kilometer to enter the congestion zone for free. Those were almost entirely hybrid cars.

That plan was supplanted in July 2013 by an Ultra-Low Emission Discount plan that only allows cars or vans with CO2 emissions of 75 g/km or less to enter for free—and they must meet Euro 5 emission limits as well.

But owners of cars in the 75-to-100 g/km band were given a two-year grace period, which is now coming to an end.

Not only hybrids but even ultra-efficient European small diesel cars fall above the 75 g/km limit, so pretty much any car that will be let in free is now going to have a plug.

At the end of June, many hybrid drivers will be "waking up to a bit of a ‘hybrid hangover’," noted Nissan's Edward Jones, "facing ongoing costs of almost £3,000 a year to drive [their] cars into the Congestion Charge zone."

Nissan is more than happy to help with the hangover.

After all, sometimes finding a nice new paramour is the best way to recover from being dumped by the old one.